free transmission education - PeachParts Mercedes-Benz Forum

blueranger · #1 10-27-2005, 02:29 AM

when i first got my 300sd 1983 i noticed it was slow on
the start up... and someone told me i should be rough with it...
so i started kicking the fuel pedal to the floor on take offs...

This destroyed the kick down switch which over time destroyed my engine.
this has gone on over a year... so it took time to learn all this..

the kick down switch is under the gas pedal mounted in the floor..
if you have any kind of tranny problems replace this first.. its cheap..
and its the problem...catch it early...

after all the shifting problems... came slipping and not shifting into 4th gear.
the reason the tranny does not shift into 4th is the vac control on top of the fuel distributor... it is not going to zero vac to allow it to go to 4th gear.. i
can disconnect it and 4th gear comes every time....so i need to adjust this or replace it....

the mercedes transmission is like a violin and it is a combination of tuning the kick down switch, the vac control and the bowdine cable... (on top of the valve cover) faliure to keep these in line will result in clutch slippage and burnt trans fluid.. which i have....

I am still using my tranny because of Trans X and mobil 1 ATF both of these will swell clutches and give you more time on your old transmission... i have an old electric fuel pump and a plastic hose i stick into the dip stick and pump out the fluid about once a week and so far the swollen clutches are still working...

pawoSD · #2 10-27-2005, 03:07 AM

How would a destroyed kickdown switch destroy the engine? Unless you overrevv'd....(don't see how) or lugged it constantly......but I often accelerate (slowly) from 20mph to 55 in 4th gear without doing a kickdown because traffic is slow enough to do so. I overall maybe use it 2-3 times a day in normal driving. Especially since I drive in "S" most of the time in the city, and never use 4th gear anyways.

How does Mobil 1 + trans-X swell clutches...aren't they metal?

I am using Mobil 1, and overall it shifts better, but its quirks are still there.

#3 10-27-2005, 06:38 AM

My experience is lots of unsuccessful troubleshooting. I will venture to guess that "not going to zero vac" is not what is preventing it from going into fourth. Zero vac, which can be considered max vac release from the plastic valve on top of the IP, happens at full throttle, or at the minimum, 3/4 throttle. So what if the car is driven at half throttle until it reaches 40-55mph? It should shift into fourth.
As far as swelling the seals. Lucas trans fluid works great. It smells and looks like atf but has the viscosity of 90w. I had a sd that would never go into fourth once it was warmed (=thinner fluid), just spun as if in neutral. It went into fourth with 2-3 quarts of lucas trans fluid in place of atf. I had nothing to lose, the trans was basically shot. I would use less than 2-3 quarts if I was worried about ruining a good trans. Ended up buying a new trans and it was very disappointing since I didn't have correct vacuum it didn't shift nice. It was improved in bits and pieces but never perfected and then the car was sold. Thought I was going to hold out for a manual trans car after that. It was a combination of thinking that I can somehow now fix vacuum issues and that manuals are so hard to find (or too expensive), bought another auto. No test drive prior to commiting to buy. Hard 1-2 and goes right to 3rd. I hope this isn't causing damage. Once the trans breaks, it will likely be parked until a manual conversion is done. If I had complete control of how it shifted mabee a new automatic would be an option.

1984 300d (210k +/-)

#4 10-27-2005, 08:42 PM

I have an 82 300sd and the trans shifts funny too. usually rough and occasionally a flair, but it is rare. The 1st to 2nd is rough 2-3 not so bad and 3-4 ok. and, when I come to a stop, there is a loud clunk noise. seems to be from 2-1 downshift. Whats up with this? thanks. zach

Hatterasguy · #5 10-27-2005, 08:52 PM

As long as you do not over rev the engine and the trans is in good shape their is no way a kick down switch or the use of one can hurt the driveline.

MB overbuilt the drivelines of these cars and besides diesels don't put out enough power to hurt them.